The children are to come in comfortable clothes and running shoes, having consumed no more than a light meal and having had pulmonary medications withdrawn as described above. A parent, a pediatric pulmonary physician and a technician is present throughout the test. Each child undergoes a physical examination to exclude evidence of wheeze, and baseline spirometry was performed. The children are asked to run freely back and forth (without a nose-clip) in a 50m long corridor next to the pulmonary laboratory. The target is to achieve 6 minutes of "free run" to increase hart-rate to 80% in the maximum for at least 4 minutes according to ATS/ERS recommendations for exercise challenge test in older children [1]. An adult (parent/technician/ physician) will run with the child to encourage him/her to continue running. Heart-rate and O2-saturation is monitored continuously throughout the run using a portable mobile pulse-oximeter monitor (Nonin medical, INC, model 2500, Minneapolis, USA).